T&T: Battery Charging Questions

[Dave Cooper]

<Rodger wrote: Sorry I've gotta disagree with your charge rate figure.
T-105s are rated at 220 AH so with 4 in series parallel john has a 440AH
bank. So if you use 20% (I use 25%) with your calcs it would be 88 amps.>



Opps, sorry I live in a 24 volt world..aka 44 amps ;-) I think at 125
degrees it would be closer to = that.



In any case the 125 degrees is too hot for batteries both for longevity and
safety. It may be OK if you are diligent on the watering and general care of
them but this temp wouldnt allow any headroom for something to go wrong,
IMHO.



To quote a statement from a solar energy site: Battery life is reduced at
higher temperatures - for every 15 degrees F over 77, battery life is cut in
half. This holds true for ANY type of Lead-Acid battery, whether sealed,
gelled, AGM, industrial or whatever. So for long life a cooler battery bank
is far better.



You need to get some air around the batteries if they are consistently this
hot.a battery that starts a thermal run away isnt a pleasant experience.



With a tight aka cheek to cheek battery bank the inner cells are going to
much higher temp than the outer cells. The only way to really tell the cell
temp is with a direct thermometer in the electrolyte or using a IR temp gun
to look at the acid while the cap is off. Anymore than a 5 degree temp
difference is reason for concern and need to be corrected. You do wear
safety glasses and gloves while messing about the batteries as a matter of
keeping those eyes working well and the skin on the hands, right?



Running any charger without temp compensation on a bank is not a good idea,
IMO. Doing so on a bank with a static temp of 125 degrees is walking the
razors edge, IMHO. Batteries have an incredible amount of power stored in
them. They also have some very bad ingredients inside those benign looking
cases. Having them go ugly and getting out isnt something you want to
happen.



As Mike said the other daylots of opinions from folks who have good
ideas..OTOH let me say again you really really dont want to flirt with a
thermal runaway. I will absolutely ruin your week and if you and the boat
survive you can call your insurance agent hopefully not from the hospital.



We live even a bit south of most folks on the list and the boat is in 85
degree water. If our engine room temp approaches 110 degrees, its normally
105,  Im worried. Extended elevated engine room temps shortens the life of
everything. Time to get better ventilation in the ER to drop the temp, IMHO.



As always YMMV..



Dave & Nancy

Swan Song

Roughwater 58

Caribbean Cruise '07